A team of researchers at the Relativistic Heavy Ion Collider (RHIC), a U.S. At the DOE’s Brookhaven National Laboratory, the Office of Science user facility has discovered conclusive evidence for two physics events anticipated more than 80 years ago. The findings, which were reported in Physical Review Letters, came from a thorough examination of more than 6,000 pairs of electrons and positrons generated in glancing particle collisions at RHIC.
The main result is that by colliding incredibly powerful photons, which are quantum “packets” of light, it is possible to directly produce pairs of electrons and positrons, particles of matter and antimatter. The fact that energy and matter (or mass) may be interchanged, according to Einstein’s famous E=mc2 equation, is what causes this conversion of energetic light into matter. Nuclear processes often transform materials into energy, both in the sun and in nuclear power plants. Now, scientists have made the direct conversion of light energy into matter.
The second finding demonstrates how the polarisation of light affects how it bends as it passes through a magnetic field in a vacuum. Birefringence, or such polarization-dependent deflection, happens when light passes through certain materials. This is the first demonstration of polarization-dependent light-bending in a vacuum, although the result is comparable to the way wavelength-dependent deflection breaks white light into rainbows.
The Solenoid Tracker at RHIC, which is the STAR detector at RHIC, must be able to monitor the angular distribution of particles created in glancing collisions of gold ions travelling at almost the speed of light in order to provide both results.
interacting photon clouds
When scientists Gregory Breit and John A. Wheeler initially proposed the speculative notion of colliding light particles to produce pairs of electrons and their antimatter counterparts, known as positrons, in 1934, such capabilities weren’t available.
Breit and Wheeler had acknowledged in their study that this is practically hard to do, according to Brookhaven Lab physicist Zhangbu Xu, a participant in RHIC’s STAR Collaboration. Lasers weren’t even invented yet! However, Breit and Wheeler suggested accelerating heavy ions as a substitute. And their substitute is exactly what RHIC is doing.
In essence, an ion is an atom that has been stripped of all of its electrons. With 79 protons, a gold ion has a strong positive charge. When a heavy ion is accelerated to such high speeds, a strong magnetic field is created that spirals around the moving particle, simulating current running through a wire.
The intensity of the circular magnetic field may be equivalent to the strength of the perpendicular electric field, according to Xu, if the speed is high enough. A photon, a quantized “particle” of light, is that configuration of parallel, equally strong electric and magnetic forces. Therefore, the gold nucleus is surrounded by a number of photons that are travelling with it like a cloud as the ions approach the speed of light.
At RHIC, researchers use two accelerator rings to accelerate gold ions to 99.995% the speed of light.
According to Xu, “We have two clouds of photons travelling in opposing directions with enough energy and intensity that the photon fields can interact when the two ions skim by each other without colliding.”
The expected electron-positron couples were sought after by STAR physicists who monitored the interactions.
However, a number of processes at RHIC, including the creation of “virtual” photons, a form of photon that persists momentarily and has an effective mass, can produce such particle pairs. Scientists must show that the presence of “virtual” photons has no impact on the experiment’s results in order to be certain that the matter-antimatter couples originated from actual photons.
The angular distribution patterns of each electron in relation to its companion positron were examined by the STAR scientists in order to achieve this. These patterns are different for pairs generated by interactions between actual and virtual photons.
“We also measured all of the systems’ energy, mass, and quantum numbers. The STAR data on this finding were examined by Daniel Brandenburg, a Goldhaber Fellow at Brookhaven Lab, who found that they are compatible with theory estimates for what would occur with actual photons.
Other researchers have explored employing strong lasers—focused streams of bright light—to produce electron-positron couples from light collisions. However, Brandenburg said that the individual photons inside those powerful beams do not yet possess sufficient energy.
Using a nonlinear technique, one experiment at the SLAC National Accelerator Laboratory in 1997 was successful. One laser beam there had to first be collided with a strong electron beam in order to increase the energy of the photons in it. collisions between numerous photons produced by the boosted photons and another laser that produced matter and antimatter in a massive electromagnetic field.
According to Breit and Wheeler’s original predictions, Brandenburg’s findings “provide clear evidence of direct, one-step creation of matter-antimatter pairs from collisions of light.” “We are able to analyse all the kinematic distributions with high statistics to determine that the experimental results are indeed consistent with real photon collisions,” the authors write. “This is made possible by the high-energy heavy ion beam of RHIC and the large acceptance and precision measurements of the STAR detector.”
